Single-strip molding apparatus

ABSTRACT

An apparatus for molding electronic components. The single-strip molding apparatus has a mold die formed from two mold halves which are movable relative to each other and can be closed upon one another. A leadframe for the component to be molded is placed into a recess in one of the mold halves. Molding material is heated and forced under pressure into the recess containing the leadframe. After the component is molded the mold is opened and the upper half of the mold is cleaned by a combined cleaning-discharge unit. Upon the return stroke of the cleaning-discharge unit, the molded component is removed and the lower half of the mold is cleaned.

BACKGROUND OF THE INVENTION

For the molding of electronic components, chips, molding apparatus areused wherein a so-called leadframe supporting an electronic component,such as a chip is placed into a mold wherein the mold displays recessesfor receiving the parts for molding, and in addition cavities arearranged in the mold wherein measured quantities of molding material areplaced and wherein by supplying heat and exerting pressure in thesecavities the molding material becomes liquid, moves via channelsintended for that purpose to the parts for molding and, curing there,encapsulates the leadframe. The leadframe is subsequently removed fromthe molding apparatus and subjected to further processing. An apparatusof this type is known for example from Patent Abstracts of Japan, vol.4, No. 128 (M-31)(610), Sep. 9, 1980, & JP,A, 5587517 of Jul. 2, 1980.

SUMMARY OF THE INVENTION

The object of the invention is to provide a single-strip moldingapparatus which combines a simple construction with a relative highproduction rate.

This achieved according to the invention by providing a single-stripmolding apparatus comprising a mold formed by two mold halves verticallymovable relative to one another and closable onto one another, means forplacing a leadframe supporting an electronic component into one of themold halves, means for carrying molding material into cavities of themold, means for exerting pressure and supplying heat to said cavities toliquify the molding material and channels for supplying said moldingmaterial to said recesses, means for heating the mold halves, means forcleaning the mold halves and means for removing a molded product fromthe mold.

By combining different processes such as cleaning, which has to takeplace after each molding cycle, with the removal of the molded productan optimal production rate is achieved.

From U.S. Pat. No. 3,059,305 a molding apparatus is known in which areciprocating hopper is provided that combines the function of supplyingmolding material and cleaning of the mold cavity. After molding theobject the molding pushes the product outwardly of the mold and cleansthe mold cavity. The mold press consists of two plungers pressing themolding material in the cavity.

According to a preferred embodiment the cleaning-discharge unit performsa reciprocating movement and during the outward movement the one moldhalf is cleaned and during the inward movement the molded product isremoved and the other mold half cleaned in one operating stroke.

An optimal production rate is achieved by setting into operation themeans for placing a subsequent leadframe in a mold immediately followingthe inward movement of the cleaning-discharge unit.

The means for exerting pressure preferably consist of at least oneplunger which is driven by means of an electromotor, a screwed rod and anut arranged on a screwed rod. Driving has taken place to date in theusual manner with hydraulic means, which however entails variousdrawbacks. Hydraulic driving requires cooling and is not otherwise wellcompatible with the clean surroundings in which the process must takeplace. There has further been the drawback that there was no directproportional relation between the exerted hydraulic pressure and/or thecontrolled volume flow of the hydraulic oil and the displacement speedof the plunger. The pressure-raising process was difficult to control.Using the electromechanical driving a direct relation is achievedbetween the action of the electromotor and the displacement speed of theplunger and/or the force to be exerted by the plunger on the moldingmaterial by converting the rotation movement of the electromotor into alinear movement of the plunger rod using the nut and the screwed rod. Anelectromotor moreover does not pollute the surrounding area which befitsthe cleanliness required of the area wherein the process takes place. Inaddition the energy consumption of a hydraulic plunger drive is muchgreater than that of an electromechanical plunger drive. With hydraulicplunger driving cooling is therefore needed for the oil heated byfriction losses. The noise level of an electromechanical driving is alsoconsiderably lower.

The mold halves are also preferably closed relative to one another by anangle lever system connected to one of the mold halves and driven by anelectromotor and a screwed rod. The required closing force to be exertedon the mold halves is transmitted in a suitable manner by the anglelevel system since this exerts great force especially at the end of thestroke.

As first alternative embodiment the mold halves can be moved relative toone another using a control mechanism consisting of a pneumatic cylinderwhich effects the largest part of the stroke and a piston-cylinder unithaving multiple pistons placed on the piston rod for providing bypneumatic means the final necessary closing force.

As second alternative embodiment the mold halves can be moved relativeto one another using a control mechanism consisting of at least onepneumatic cylinder which effects the largest part of the stroke and aclosed piston-diaphragm cylinder unit filled with liquid for convertingpneumatic pressure into hydraulic pressure for providing the finalnecessary closing force.

With the apparatus according to the invention the mold halves perform avertical movement relative to one another, the lower mold half isfixedly disposed, the upper half is movable and the means for cleaning,for placing the leadframe in the mold and for removing product out ofthe mold perform a horizontal movement and the means unified into acleaning-discharge unit for cleaning and removal of the product from theone side and the means for placing the leadframe from the other sideperform a reciprocating movement extending into the mold die. Thisprovides the advantage that during the discharge movement of thefinished product to the one side following on therefrom the input meanscan place a subsequent leadframe in the mold die.

The means for placing a leadframe are formed by a first carriage movableover guide rails while the cleaning-discharge unit is placed on a secondcarriage which is movable over the same guide rails.

The plunger increasing the pressure in a cavity is preferably underbias. It is hereby possible to raise the pressure to the required leveldespite the fact that the same quantity of molding material will notalways be present in the relative cavity. The position of the plunger istherefore adapted by the bias to the volume of molding material in therelevant cavity. As alternative method a channel is arranged in one ofthe two mold halves which mutually connects the cavities into which themeasured quantities of molding material are fed, with the object ofequalising mutual volume-differences in these fed quantities of moldingmaterial.

The invention will be further elucidated with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 show schematically one complete cycle of the molding apparatusaccording to the invention.

FIG. 4 shows a perspective view of the molding apparatus according tothe invention.

FIG. 5 shows on a larger scale a detail of the lowermost part of themolding apparatus according to FIG. 4.

FIG. 6 shows a sectional view of the mold of the molding apparatus fromFIGS. 4 and 5.

FIG. 7 shows a first alternative embodiment of the closing mechanism ofthe mold of the molding apparatus according to the invention. and

FIG. 8 shows a second alternative embodiment of the closing mechanism ofthe mold of the molding apparatus according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 the mold, which consists of a fixedly positioned lower halfand a vertically movable upper half, is open. It is assumed that themolding has been completed during the previous cycle and that the moldedproduct 3 is still in the mold, that is, in the lower half 1. Thecleaning-discharge unit 4 consists of a discharge carriage 5 and abrushing device 6 with brushes at the top 7 and brushes at the bottom 8.After opening of the mold (FIG. 1) the cleaning-discharge carriage 4performs a movement to the left and thereby cleans the upper half of themold (FIG. 2). The input carriage 9 likewise moves to the left to pickup a subsequent leadframe 10 from a store (not drawn) by means of a feedbelt 16.

According to FIG. 2 the cleaning-discharge unit 4 then performs thereturn stroke wherein the discharge carriage 5 picks up the finishedmolded frame 3 using schematically designated hook-shaped means 11, 12and cleans the lower half of the mold.

Following on from the active stroke shown in FIG. 2 the input carriage 9places the next leadframe into the mold. During the position in FIG. 1the input carriage is thereby filled in cavities arranged for thispurpose from a so-called pellet carriage 13 with pellet-shaped portionsof molding material which in the position as in FIG. 3 are placed intothe cavities 14 intended for this purpose in the lower half 1 of themold. The upper half 2 of the mold subsequently moves in the downwarddirection indicated with an arrow and closes (not drawn) onto the lowermold half, whereupon the molding process beings. In the position drawnin FIG. 3 remnants of the molding pellets are removed from the leadframe3 with schematically designated means 15, after which the leadframe isdischarged via a belt 17.

A further more detailed description will now be given with reference toFIGS. 4 and 5.

Mounted on the frame 100 of the machine is a fixedly positioned table101. The table 101 bears a fixed lower mold half 102. The upper moldhalf 103 is movable relative to the lower half 102 using pull rods 104,105 which are connected to the upper half 103 by the respective nutconnections, 106, 107. The pull rods 104, 105 are movable relative tothe fixed table 101 via bearings, for example 108.

The driving of the upper half of the mold 103 takes place from anelectromotor 109. Driven by means of the worm box 110 are the anglelevel systems 111, 112. The angle lever systems are coupled on the oneside to a movable underplate 113 and on the other side to a plate 116fixedly connected to the table 101 by means of columns 114, 115. Whenthe electromotor rotates the underplate 113 is moved vertically, forexample in the direction of the arrow P1, which movement is transmittedvia the pull rods 104, 105 onto the upper mold half 103. At the end ofthe stroke the arms of the angle lever system 111, 112 lie practicallyin one line so that a very great closing force is achieved.

The input carriage 117 is movable over the guide rails 118, 119. Thedriving of the input carriage 117 takes place from the electromotor 120.

Leadframes are supplied from a supply cassette and are carried up overthe belts 122, 123 as far as a stop 124. During the position of theinput carriage outside the mold the input carriage is filled from aso-called pellet-filling carriage 125 with pellet-shaped moldingmaterial which is take from a supply reservoir 126. For a reliabletake-over of pellet-shaped molding material by the input carriage 117from the pellet transporting carriage 125 use is made in both carriagesof pin-shaped guiding means 127. The mutual movements are controlledusing a sensor 128.

The cleaning-discharge unit 129 is likewise movable over the rails 118,119 between the position outside the mold die and the position insidethe mold die. The unit 129 consists of a cleaning-brushing device 130and a discharge member 131. The cleaning device 130 brushes both moldhalves after use and simultaneously sucks up brushed-off remnants.Co-acting with the unit is a break-off plate 132 which subjects thefinished product to an after-processing.

As can be seen in FIG. 5, the cavities 133 in the lower half 102 of themold are each provided with a plunger 134 which (see also FIG. 6) isbiased by a spring washer 135 such that the position of the plunger isadapted to the quantity of molding material in the relevant cavities133. The plungers are driven from an electromotor which drives a screwedrod 137 via the speed control 136. A nut 138 is placed on the screwedrod so that the rotating movement is converted into a verticallydirected movement of the frame 139. Fixedly coupled to the frame are thedrive rods 140, 141 for the plunger bracket 142 which in turn drives theplungers. As can be seen from the section VI--VI in FIG. 5 shown on alarger scale in FIG. 6, the pellet-shaped molding material 143 iscompressed during the ascending movement and transported via the channel144 to the cavity 145 in the lower half of the mold where the chip 146is arranged. As can be further seen in FIG. 6 a heating coil 147 isarranged for heating the lower half of the mold. The lower half of themold is insulated by means of insulating material 148. Also visible inFIG. 6 is the protective cover 149.

In order to improve removal of the finished product a push-out pin 150under bias of a spring 151 is arranged near the cavity 145.

The embodiment according to FIG. 7 shows another embodiment fordisplacement of the upper half of the mold and the generating of therequired great closing force.

Pneumatic cylinders 152 and 153 displace the upper half of the mold viathe movable underplate 113, as in the case of the first discussedembodiment. At the end of the stroke the slide 153 is pushed under thepiston rod 154 so that a closed piston-plunger 155 is created. Via thechannel compressed air is subsequently admitted from a source 156 (notdrawn) which is distributed via the sub-channels, for example 157, overpistons, for example 158, arranged on the piston rod 154. As a result ofthe large suction surface obtained by the combination of the pistons 158arranged parallel on the rod 154 a very great closing force is achievedwith a small stroke. This is transmitted to the plate 113 and thereforeto the upper half of the mold 103. It is further noted that the closingof the slide takes place by means of the plunger 160.

FIG. 8 shows an alternative embodiment of the closing mechanism of themold of the mold apparatus according to the invention.

A discussion of those parts which correspond with the embodimentaccording to figure 7 is omitted.

The closing force to the mold halves is provided in this case by apiston-diaphragm cylinder unit filled with liquid. The plunger 161 ismoved by the pressure of the liquid exerted on the piston 162, which isderived from the control cylinder 163. This is in contact with thecylinder space of the plunger 161 via the line 156.

Preferably a device 200 for measuring the closing force of one of thehalves of the molds is with respect to the other mold half is providedin the linkage for transferring the force from the electromotor to themovable mold half. Upon receiving a predetermined value of the closingforce, a control signal is generated that is applied to stop the drivingelectromotor.

We claim:
 1. A single-strip molding apparatus, comprising:a mold formedby an upper mold half and a lower half vertically movable relative toone another and closable onto one another; means for placing a leadframesupporting an electronic component into a recess in one of the moldhalves; means for carrying molding material into a cavity of the mold;means for exerting pressure and supplying heat to said cavity to liquifythe molding material; channels for supplying said liquified moldingmaterial to said recess; means for heating the mold halves; means forcleaning the mold halves; and means for removing a molded product fromthe mold, wherein the means for cleaning and for removing the moldedproduct are unified into a cleaning-discharge unit which removes theproduct from one side of the mold while said means for placing theleadframe supplies said leadframe from another side of the mold, andfurther, wherein said cleaning discharge unit and said means for placingthe leadframe perform reciprocating movements into the mold.
 2. Theapparatus of claim 1, wherein the cleaning-discharge unit performs areciprocating movement which includes a forward and a backward movementand during the backward movement the upper mold half is cleaned andduring the forward movement the molded product is removed from the moldand the lower mold half is cleaned.
 3. The apparatus of claim 1, whereinimmediately following the forward movement of the cleaning-dischargeunit the means for placing a leadframe into the mold becomes operative.4. The apparatus of claim 1 wherein the means for exerting pressure tothe cavity consists of a plunger which is driven by means of anelectromotor, a screwed rod and a nut arranged on the screwed rod. 5.The apparatus of claim 1, wherein the upper and lower mold halves areclosed relative to one another by an angle lever system connected to theupper mold half and driven by an electromotor over a screwed rod.
 6. Theapparatus of claim 1, wherein the upper and lower mold halves are movedrelative to one another using a control mechanism consisting of apneumatic cylinder and a closed piston-diaphragm cylinder unit filledwith liquid for providing the closing force.
 7. The apparatus of claim1, wherein the means for placing a leadframe into the mold are formed bya first carriage movable over guide rails and the cleaning-dischargeunit is placed on a second carriage movable over the guide rails.
 8. Theapparatus of claim 1, wherein the plunger increasing the pressure in acavity is under a bias force.
 9. The apparatus of claim 1, wherein thereis more than one cavity and the plungers increasing the pressure in thecavities are mutually connected by means of channels in one of the moldhalves.
 10. The apparatus of claim 1, further comprising:means formeasuring the closing force of the mold halves.
 11. The apparatus ofclaim 10, wherein said means for measuring the closing force are adaptedto produce a control signal to stop the electromotor for driving saidangle lever system connected to one of the mold halves when said closureforce reaches a predetermined value.
 12. The apparatus of claim 2,wherein immediately following the forward movement of thecleaning-discharge unit the means for placing a leadframe into the moldbecomes operative.
 13. The apparatus of claim 2, wherein the means forexerting pressure to the cavity consists of a plunger which is driven bymeans of an electromotor, a screwed rod and a nut arranged on thescrewed rod.
 14. The apparatus of claim 2, wherein the upper and lowermold halves are closed relative to one another by an angle lever systemconnected to the upper mold half and driven by an electromotor over ascrewed rod.
 15. The apparatus of claim 2, wherein the upper and lowermold halves are moved relative to one another using a control mechanismconsisting of a pneumatic cylinder and a closed piston-diaphragmcylinder unit filled with liquid for providing the closing force. 16.The apparatus of claim 2, wherein the means for placing a leadframe intothe mold are formed by a first carriage movable over guide rails and thecleaning-discharge unit is placed on a second carriage movable over theguide rails.
 17. The apparatus of claim 2, wherein the plungerincreasing the pressure in a cavity is under a bias force.
 18. Theapparatus of claim 2, wherein there is more than one cavity and theplungers increasing the pressure in the cavities are mutually connectedby means of channels in one of the mold halves.
 19. The apparatus ofclaim 2, further comprising:means for measuring the closing force of themold halves.
 20. The apparatus of claim 19, wherein said means formeasuring the closing force are adapted to produce a control signal tostop the electromotor for driving said angle lever system connected toone of the mold halves when said closure force reaches a predeterminedvalue.
 21. An apparatus for encapsulating or molding an electroniccomponent comprising:a mold having an upper first mold half and a lowersecond mold half, the mold halves being vertically movable relative toone another and closable onto one another, the lower mold half having arecess; reciprocating means for placing an electronic component into therecess of the lower mold half; means for providing molding material in aliquified form to the recess; means for curing the molding material; anda reciprocating cleaning-discharge unit having a forward movement intothe mold and a backward movement out of the mold, the cleaning-dischargeunit including means for cleaning the upper mold half and the lower moldhalf and means for removing the component from the mold after themolding material has been cured, wherein during the backward movementthe upper mold half is cleaned and during the forward movement themolded product is removed from the mold and the lower mold half iscleaned, and further wherein the means for removing the molded componentremoves the component from one side of the mold while the means forplacing the electronic component into the recess supplies the componentfrom another side of the mold.